A Tour of the Cell

Chapter 6

Objectives Distinguish between a prokaryotic and eukaryotic cell Describe the unique structures of a prokaryotic cell Describe the structural differences between plant and

animal cells Describe the complex structural and functional

interconnections among the organelles of the endomembrane system

Describe the structure of the eukaryotic nucleus, mitochondrion and chloroplast

Describe the surface structures of the cell that provide support, protection, and movement in, and communication with, the extracellular environment

Introduction Cell is smallest functional unit of life

cell theory:• all organisms composed of cells• all existing cells arise from pre-existing cells

Common characteristics of all cells: cell contents surrounded by plasma membrane cytoplasm consists of semifluid matrix organelles are embedded in cytoplasm contain genes in the form of DNA

Fundamental Features of Life

Features of cells are characteristic of life cells are highly structured cell structure and function are related cell membranes separate the cell from the

external environment each cell has DNA as the genetic material each cell carries out metabolism

Cell Organization

Two types of cells-prokaryotic and eukaryotic

Prokaryotic: small lacks nucleus; DNA in nucleoid region cytoplasm surrounded by plasma membrane

and outer cell wall flagella and pili may be present

Cell Organization

Eukaryotic Larger than prokaryotic cells complex internal structure with membranous and non-

membranous organelles Membranous components: nucleus, endoplasmic

reticulum, Golgi apparatus,mitochondria, lysosomes and peroxisomes

Non-membranous components: ribosomes, microtubules, centrioles, flagella and cytoskeleton

Plant vs. Animal Cells

Animal cells surrounded by plasma membrane only

Plant cells surrounded by plasma membrane and rigid cell wall; also have central vacuole and chloroplasts

Eukaryotic Cell Organization

Eukaryotic organelles form four functional groups: manufacture breakdown energy processing support, movement and communication

Manufacturing

Nucleus is cell’s genetic control center surrounded by double membrane

contains pores to allow passage of material between nucleus and cytoplasm

DNA normally present as strands of chromatin

During cell division, chromatin coils up to form chromosomes

Nucleolus-organelle within nucleus-responsible for ribosomal RNA synthesis

Endomembrane system

Collection of membranes either inside or Collection of membranes either inside or surrounding the eukaryotic cell, related through surrounding the eukaryotic cell, related through direct physical contact or by transfer of vesiclesdirect physical contact or by transfer of vesicles

Endomembrane system

Endomembrane system: RER and SER

Rough endoplasmic reticulum contains ribosomes; protein synthesis ( RER)

Smooth endoplasmic reticulum synthesizes lipids, processes materials, acts as storage and detoxifies substances (SER)

Golgi Golgi apparatus recieves products from ER

Chemically modifies the products sent to it

Puts “Zip Codes” on products so they know where to go in the cell

Puts these modified products in vesicles and sends them out

Golgi

The Golgi Apparatus is the “UPS” of the cellThe Golgi Apparatus is the “UPS” of the cell

Its recieves, warehouses, sorts, modifies, packs and Its recieves, warehouses, sorts, modifies, packs and reships substancesreships substances

Lysosomes

Lysosomes contain enzymes to digest substances and wastes; defective lysosomes cause fatal diseases

Lysosomes help your cells recycle materials: Each Liver cell recycles half of its synthesized macromolecules per week

Whey else do they do?

Vacuoles

Vacuoles function in general cell maintenance

In plants they can hold organic substances

In protists vacuoles can hold food or water, or act as pumps

Energy Processing

Mitochondria: found in all eukaryotic cells, except anaerobic

protozoans surrounded by double membrane site of cellular respiration Prokaryotes don’t have them… What do they do?? Inner and outer membrane Matrix and Cristae

Chloroplasts Chloroplasts:

found in plants and algae convert solar energy to chemical energy Surrounded by double membrane site of photosynthesis

More on these organelles in Ch 10

Peroxisomes

What is the function of Peroxisomes?What is the function of Peroxisomes?

Read all about them in your bookRead all about them in your book

What is the difference between the terms What is the difference between the terms detoxification and degredation???detoxification and degredation???

Support, Movement, and Communication

Internal cell skeleton-cytoskeleton composed of 3D meshwork of proteins rods of globular proteins-microfilaments

ropelike strands of fibrous proteins-intermediate filaments hollow tubes of globular proteins-microtubules

microtubules provide anchors for organelles, act as conveyor belts and form cilia and flagella

Cilia and flagella function to move whole cell structure consists of 9 microtubule doublets

arranged around central pair (9+2)

Movement of cilia and flagella occurs when arms consisting of the protein dynein move the microtubule doublets past each other

Microfilaments cause contraction of muscle cells

They also function in ameboid movement, cytoplasmic streaming and support for cellular projections

Centrioles

Centrioles, located adjacent to the nucleus, anchor and organize the microtubules that form the spindle during cell division

Eukaryotic Cell Organization

Cell surfaces protect, support and join cells in plants, neighboring cells joined to form

interconnected and coordinated group cell walls multi-layered, composed of mixtures of

polysaccharides and proteins plasmodesmata-channels through cell walls connecting

cytoplasm of adjacent cells- plants

Extracellular Matrix

in multi-cellular animals cells often surrounded by sticky mixture of polysaccharides and proteins

Extends outward from the cell membrane

Lots of collagen is found there……

Eukaryotic Cell Organization

Several type of junctions between cells: tight junctions: leak proof; block movement of

substances

anchoring junctions- join cells and provide structural support; like the rivets in your blue jeans

communicating junctions ( gap junctions)-provide channels between cells; allow rapid transport of materials